title	description	ms.topic	ms.date	ms.devlang	ms.custom	zone_pivot_groups
Azure Blob storage output binding for Azure Functions	Learn how to provide Azure Blob storage output binding data to an Azure Function.	reference	03/02/2023	csharp	devx-track-csharp, devx-track-python, devx-track-extended-java, devx-track-js, devx-track-ts	programming-languages-set-functions

Azure Blob storage output binding for Azure Functions

The output binding allows you to modify and delete blob storage data in an Azure Function.

For information on setup and configuration details, see the overview.

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Example

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[!INCLUDE functions-bindings-csharp-intro]

[!INCLUDE functions-in-process-model-retirement-note]

Isolated worker model

The following example is a C# function that runs in an isolated worker process and uses a blob trigger with both blob input and blob output blob bindings. The function is triggered by the creation of a blob in the test-samples-trigger container. It reads a text file from the test-samples-input container and creates a new text file in an output container based on the name of the triggered file.

:::code language="csharp" source="~/azure-functions-dotnet-worker/samples/Extensions/Blob/BlobFunction.cs" range="4-26":::

In-process model

The following example is a C# function that runs in-process and uses a blob trigger and two output blob bindings. The function is triggered by the creation of an image blob in the sample-images container. It creates small and medium size copies of the image blob.

usingSystem.Collections.Generic;usingSystem.IO;usingMicrosoft.Azure.WebJobs;usingSixLabors.ImageSharp;usingSixLabors.ImageSharp.Formats;usingSixLabors.ImageSharp.PixelFormats;usingSixLabors.ImageSharp.Processing;publicclassResizeImages{[FunctionName("ResizeImage")]publicstaticvoidRun([BlobTrigger("sample-images/{name}")]Streamimage,[Blob("sample-images-sm/{name}",FileAccess.Write)]StreamimageSmall,[Blob("sample-images-md/{name}",FileAccess.Write)]StreamimageMedium){IImageFormatformat;using(Image<Rgba32>input=Image.Load<Rgba32>(image,outformat)){ResizeImage(input,imageSmall,ImageSize.Small,format);}image.Position=0;using(Image<Rgba32>input=Image.Load<Rgba32>(image,outformat)){ResizeImage(input,imageMedium,ImageSize.Medium,format);}}publicstaticvoidResizeImage(Image<Rgba32>input,Streamoutput,ImageSizesize,IImageFormatformat){vardimensions=imageDimensionsTable[size];input.Mutate(x =>x.Resize(dimensions.Item1,dimensions.Item2));input.Save(output,format);}publicenumImageSize{ExtraSmall,Small,Medium}privatestaticDictionary<ImageSize,(int,int)>imageDimensionsTable=newDictionary<ImageSize,(int,int)>(){{ImageSize.ExtraSmall,(320,200)},{ImageSize.Small,(640,400)},{ImageSize.Medium,(800,600)}};}

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This section contains the following examples:

HTTP trigger, using OutputBinding (Java)

The following example shows a Java function that uses the HttpTrigger annotation to receive a parameter containing the name of a file in a blob storage container. The BlobInput annotation then reads the file and passes its contents to the function as a byte[]. The BlobOutput annotation binds to OutputBinding outputItem, which is then used by the function to write the contents of the input blob to the configured storage container.

@FunctionName("copyBlobHttp") @StorageAccount("Storage_Account_Connection_String") publicHttpResponseMessagecopyBlobHttp( @HttpTrigger(name = "req", methods = {HttpMethod.GET}, authLevel = AuthorizationLevel.ANONYMOUS) HttpRequestMessage<Optional<String>> request, @BlobInput( name = "file", dataType = "binary", path = "samples-workitems/{Query.file}") byte[] content, @BlobOutput( name = "target", path = "myblob/{Query.file}-CopyViaHttp") OutputBinding<String> outputItem, finalExecutionContextcontext) { // Save blob to outputItemoutputItem.setValue(newString(content, StandardCharsets.UTF_8)); // build HTTP response with size of requested blobreturnrequest.createResponseBuilder(HttpStatus.OK) .body("The size of \"" + request.getQueryParameters().get("file") + "\" is: " + content.length + " bytes") .build(); }

Queue trigger, using function return value (Java)

The following example shows a Java function that uses the QueueTrigger annotation to receive a message containing the name of a file in a blob storage container. The BlobInput annotation then reads the file and passes its contents to the function as a byte[]. The BlobOutput annotation binds to the function return value, which is then used by the runtime to write the contents of the input blob to the configured storage container.

@FunctionName("copyBlobQueueTrigger") @StorageAccount("Storage_Account_Connection_String") @BlobOutput( name = "target", path = "myblob/{queueTrigger}-Copy") publicStringcopyBlobQueue( @QueueTrigger( name = "filename", dataType = "string", queueName = "myqueue-items") Stringfilename, @BlobInput( name = "file", path = "samples-workitems/{queueTrigger}") Stringcontent, finalExecutionContextcontext) { context.getLogger().info("The content of \"" + filename + "\" is: " + content); returncontent; }

In the Java functions runtime library, use the @BlobOutput annotation on function parameters whose value would be written to an object in blob storage. The parameter type should be OutputBinding<T>, where T is any native Java type or a POJO.

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Model v4

The following example shows a queue triggered TypeScript function that makes a copy of a blob. The function is triggered by a queue message that contains the name of the blob to copy. The new blob is named {originalblobname}-Copy.

:::code language="typescript" source="~/azure-functions-nodejs-v4/ts/src/functions/storageBlobInputAndOutput1.ts" :::

Model v3

TypeScript samples are not documented for model v3.

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Model v4

The following example shows a queue triggered JavaScript function that makes a copy of a blob. The function is triggered by a queue message that contains the name of the blob to copy. The new blob is named {originalblobname}-Copy.

:::code language="javascript" source="~/azure-functions-nodejs-v4/js/src/functions/storageBlobInputAndOutput1.js" :::

Model v3

The following example shows blob input and output bindings in a function.json file and JavaScript code that uses the bindings. The function makes a copy of a blob. The function is triggered by a queue message that contains the name of the blob to copy. The new blob is named {originalblobname}-Copy.

In the function.json file, the queueTrigger metadata property is used to specify the blob name in the path properties:

{ "bindings": [ { "queueName": "myqueue-items", "connection": "MyStorageConnectionAppSetting", "name": "myQueueItem", "type": "queueTrigger", "direction": "in" }, { "name": "myInputBlob", "type": "blob", "path": "samples-workitems/{queueTrigger}", "connection": "MyStorageConnectionAppSetting", "direction": "in" }, { "name": "myOutputBlob", "type": "blob", "path": "samples-workitems/{queueTrigger}-Copy", "connection": "MyStorageConnectionAppSetting", "direction": "out" } ], "disabled": false }

The configuration section explains these properties.

Here's the JavaScript code:

module.exports=asyncfunction(context){context.log('Node.js Queue trigger function processed',context.bindings.myQueueItem);context.bindings.myOutputBlob=context.bindings.myInputBlob;};

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The following example demonstrates how to create a copy of an incoming blob as the output from a PowerShell function.

In the function's configuration file (function.json), the trigger metadata property is used to specify the output blob name in the path properties.

Note

To avoid infinite loops, make sure your input and output paths are different.

{ "bindings": [ { "name": "myInputBlob", "path": "data/{trigger}", "connection": "MyStorageConnectionAppSetting", "direction": "in", "type": "blobTrigger" }, { "name": "myOutputBlob", "type": "blob", "path": "data/copy/{trigger}", "connection": "MyStorageConnectionAppSetting", "direction": "out" } ], "disabled": false }

Here's the PowerShell code:

# Input bindings are passed in via param block.param([byte[]] $myInputBlob,$TriggerMetadata) Write-Host"PowerShell Blob trigger function Processed blob Name: $($TriggerMetadata.Name)"Push-OutputBinding-Name myOutputBlob -Value $myInputBlob

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The following example shows blob input and output bindings. The example depends on whether you use the v1 or v2 Python programming model.

v2

The code creates a copy of a blob.

importloggingimportazure.functionsasfuncapp=func.FunctionApp() @app.function_name(name="BlobOutput1")@app.route(route="file")@app.blob_input(arg_name="inputblob",path="sample-workitems/test.txt",connection="<BLOB_CONNECTION_SETTING>")@app.blob_output(arg_name="outputblob",path="newblob/test.txt",connection="<BLOB_CONNECTION_SETTING>")defmain(req: func.HttpRequest, inputblob: str, outputblob: func.Out[str]): logging.info(f'Python Queue trigger function processed {len(inputblob)} bytes') outputblob.set(inputblob) return"ok"

v1

The function makes a copy of a blob. The function is triggered by a queue message that contains the name of the blob to copy. The new blob is named {originalblobname}-Copy.

In the function.json file, the queueTrigger metadata property is used to specify the blob name in the path properties:

{ "bindings": [ { "queueName": "myqueue-items", "connection": "MyStorageConnectionAppSetting", "name": "queuemsg", "type": "queueTrigger", "direction": "in" }, { "name": "inputblob", "type": "blob", "dataType": "binary", "path": "samples-workitems/{queueTrigger}", "connection": "MyStorageConnectionAppSetting", "direction": "in" }, { "name": "outputblob", "type": "blob", "dataType": "binary", "path": "samples-workitems/{queueTrigger}-Copy", "connection": "MyStorageConnectionAppSetting", "direction": "out" } ], "disabled": false, "scriptFile": "__init__.py" }

The configuration section explains these properties.

Here's the Python code:

importloggingimportazure.functionsasfuncdefmain(queuemsg: func.QueueMessage, inputblob: bytes, outputblob: func.Out[bytes]): logging.info(f'Python Queue trigger function processed {len(inputblob)} bytes') outputblob.set(inputblob)

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Attributes

Both in-process and isolated worker process C# libraries use attribute to define the function. C# script instead uses a function.json configuration file as described in the C# scripting guide.

Isolated worker model

The BlobOutputAttribute constructor takes the following parameters:

Parameter	Description
BlobPath	The path to the blob.
Connection	The name of an app setting or setting collection that specifies how to connect to Azure Blobs. See Connections.

In-process model

The BlobAttribute attribute's constructor takes the following parameters:

Parameter	Description
BlobPath	The path to the blob.
Connection	The name of an app setting or setting collection that specifies how to connect to Azure Blobs. See Connections.
Access	Indicates whether you will be reading or writing.

The following example sets the path to the blob and a FileAccess parameter indicating write for an output binding:

[FunctionName("ResizeImage")]publicstaticvoidRun([BlobTrigger("sample-images/{name}")]Streamimage,[Blob("sample-images-md/{name}",FileAccess.Write)]StreamimageSmall){ ...}

[!INCLUDE functions-bindings-storage-attribute]

[!INCLUDE app settings to local.settings.json]

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Decorators

Applies only to the Python v2 programming model.

For Python v2 functions defined using decorators, the following properties on the blob_input and blob_output decorators define the Blob Storage triggers:

Property	Description
`arg_name`	The name of the variable that represents the blob in function code.
`path`	The path to the blob For the `blob_input` decorator, it's the blob read. For the `blob_output` decorator, it's the output or copy of the input blob.
`connection`	The storage account connection string.
`dataType`	For dynamically typed languages, specifies the underlying data type. Possible values are `string`, `binary`, or `stream`. For more detail, refer to the triggers and bindings concepts.

For Python functions defined by using function.json, see the Configuration section. ::: zone-end

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Annotations

The @BlobOutput attribute gives you access to the blob that triggered the function. If you use a byte array with the attribute, set dataType to binary. Refer to the output example for details. ::: zone-end
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Configuration

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::: zone pivot="programming-language-python" Applies only to the Python v1 programming model.

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Model v4

The following table explains the properties that you can set on the options object passed to the output.storageBlob() method.

Property	Description
path	The path to the blob container.
connection	The name of an app setting or setting collection that specifies how to connect to Azure Blobs. See Connections.

Model v3

The following table explains the binding configuration properties that you set in the function.json file.

Property	Description
type	Must be set to `blob`.
direction	Must be set to `out` for an output binding. Exceptions are noted in the usage section.
name	The name of the variable that represents the blob in function code. Set to `$return` to reference the function return value.
path	The path to the blob container.
connection	The name of an app setting or setting collection that specifies how to connect to Azure Blobs. See Connections.

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The following table explains the binding configuration properties that you set in the function.json file.

Property	Description
type	Must be set to `blob`.
direction	Must be set to `out` for an output binding. Exceptions are noted in the usage section.
name	The name of the variable that represents the blob in function code. Set to `$return` to reference the function return value.
path	The path to the blob container.
connection	The name of an app setting or setting collection that specifies how to connect to Azure Blobs. See Connections.

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See the Example section for complete examples.

Usage

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The binding types supported by blob output depend on the extension package version and the C# modality used in your function app.

Isolated worker model

[!INCLUDE functions-bindings-storage-blob-output-dotnet-isolated-types]

In-process model

See Binding types for a list of supported types.

Binding to string, or Byte[] is only recommended when the blob size is small. This is recommended because the entire blob contents are loaded into memory. For most blobs, use a Stream or BlobClient type. For more information, see Concurrency and memory usage.

If you get an error message when trying to bind to one of the Storage SDK types, make sure that you have a reference to the correct Storage SDK version.

[!INCLUDE functions-bindings-blob-storage-attribute] ::: zone-end

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The @BlobOutput attribute gives you access to the blob that triggered the function. If you use a byte array with the attribute, set dataType to binary. Refer to the output example for details.

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Model v4

Access the blob data by returning the value directly or using context.extraOutputs.set().

Model v3

Access the blob data by using context.bindings.<name> where <name> is the value specified in the name property of function.json.

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Access the blob data via a parameter that matches the name designated by binding's name parameter in the function.json file.

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You can declare function parameters as the following types to write out to blob storage:

Strings as func.Out[str]
Streams as func.Out[func.InputStream]

Refer to the output example for details.

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[!INCLUDE functions-storage-blob-connections]

Exceptions and return codes

Binding	Reference
Blob	Blob Error Codes
Blob, Table, Queue	Storage Error Codes
Blob, Table, Queue	Troubleshooting

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functions-bindings-storage-blob-output.md

functions-bindings-storage-blob-output.md

Azure Blob storage output binding for Azure Functions

Example

Isolated worker model

In-process model

HTTP trigger, using OutputBinding (Java)

Queue trigger, using function return value (Java)

Model v4

Model v3

Model v4

Model v3

v2

v1

Attributes

Isolated worker model

In-process model

Decorators

Annotations

Configuration

Model v4

Model v3

Usage

Isolated worker model

In-process model

Model v4

Model v3

Exceptions and return codes

Next steps

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functions-bindings-storage-blob-output.md

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functions-bindings-storage-blob-output.md

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Azure Blob storage output binding for Azure Functions

Example

HTTP trigger, using OutputBinding (Java)

Queue trigger, using function return value (Java)

Attributes

Decorators

Annotations

Configuration

Usage

Exceptions and return codes

Next steps